A packet switched communication network may for example be used for communication of voice or audio data. For this, transport protocols, such as the Realtime Transport Protocol (RTP), are available. For Internet Protocol (IP) telephony systems or Voice over Internet Protocol (VoIP) transmission systems, it may be desired to communicate Dual Tone Multi-Frequency (DTMF) signals over the network, for example when a user needs to interact with an automated system, for example an automated call direction system.
Usually, voice data is provided to a vocoder (voice encoder) at the sender side. The vocoder employs a compression algorithm in order to reduce bandwidth of voice data transmitted over the network, the compressed voice data being provided to an RTP encoder for generating RTP-compliant packets containing the voice data as payload. However, applying a DTMF signal to the vocoder and transmitting the DTMF signal “inband” results in degradation of the DTMF signal due to the use of the compression algorithm, the compression algorithm having been designed for compressing voice signals and not DTMF tones. In order to avoid the degradation of the DTMF signal resulting from in-band communication of the DTMF signal, the Internet Engineering Task Force (IETF) Request For Comments (RFC) 2833 or RFC 4733 provide a framework for communicating the DTMF signal “out-of-band”.
A DTMF detector is therefore employed in order to detect the DTMF signal and communicate data identifying the nature of the DTMF signal to an RFC 2833 or RFC 4733 encoder being coupled to the RTP encoder for communication of the data identifying the DTMF signal to a receiver where the DTMF signal is regenerated based upon the data identifying the DTMF signal. In order to provide uniformity in relation to DTMF signals, the Telecommunication Standardization Sector of the International Telecommunications Union (ITU-T) Recommendation Q.24 specifies certain conditions for a DTMF signal to observe in order to qualify as a valid DTMF signal.
However, false DTMF detection may result for example in sending a wrong RFC 2833 start packet or a DTMF interruption may result in sending a wrong RFC 2833 end packet, therefore probably affecting an ongoing transmission.
Furthermore, DTMF detectors are known to suffer from “DTMF leakage” which can effectively become appended to a given DTMF signal due to undetermined state periods, wherein the presence of the tone cannot be determined instantly, thereby extending the duration of the given DTMF signal.